A dart (throwing arrow) used in a dart game is configured with a metal barrel which is a portion held by a player with fingers, a point (tip) attached to a front end side of the barrel, a shaft attached to a rear end side of the barrel, and a flight (arrow feathers) attached to the shaft. The dart includes a hard dart having a metal point and a soft dart having a plastic point. Many shafts and flights are plastic.
A plastic point, a plastic shaft, and a plastic flight are likely to be damaged by a shock occurred when stuck into a dartboard or when falling to the floor. For this reason, many darts can be easily disassembled into a point, a barrel, a shaft, and a flight, and are made such that the point, the shaft, and the flight can be replaced. In general, the point and the barrel, and the barrel and the shaft are detachably fastened to each other by respectively provided threaded portions.
However, there is a problem in which fastening by the threaded portions is likely to be loosened while the throwing of the dart is repeated. In the case of a dart, the width of a thread ridge of a barrel slightly differs according to a manufacturer. For this reason, a thread ridge of a point or a shaft is designed to fit barrels of various manufacturers such that there is a clearance to a large extent with respect to the basic ridge profile. In this case, it is particularly likely to be loosened. If fastening by the threaded portions is loosened, a player is bothered by the loosening during the game and the player lose concentration in some cases.
The following is proposed as a dart in which fastening by a threaded portion is unlikely to be loosened.
(1) A dart including, in a threaded hole, a biasing member for pushing a threaded shank, which is a shaft screwed in the threaded hole of a barrel, back in a direction of separating away from the threaded hole (PTL 1).
(2) A dart in which a projection pushing a barrel back in a direction of separating away from a thread by elastic deformation is provided on a bearing surface of a point and a shaft, both of which has a threaded shank screwed into a threaded hole of the barrel (PTL 2).
In both darts of (1) and (2), by one member pushing the other member back in the direction of separating away from a thread, a large frictional force is generated between a thread ridge of the threaded shank and a thread ridge of the threaded hole. Consequently, fastening by the threaded portion is prevented from being loosened.
However, in the dart of (1), it is necessary to provide the biasing member in the threaded hole, and thus manufacturing costs of the dart increase. In the dart of (2), even if locking effects arise in a state where the barrel presses against the projection, the locking effects are lost when the barrel is even slightly separated away from the projection.
For example, although not related to a dart, the following is proposed as a fastening member in which fastening by a threaded portion is unlikely to be loosened.
(3) A fastening member which is configured such that a flank angle of one flank, out of flanks on both sides of a thread ridge of one threaded member, is smaller than a flank angle of a flank of a thread ridge of the other threaded member (basic ridge profile) (PTLS 3 and 4).
(4) A fastening member which is configured such that a slit is formed in a crest of a thread ridge of one threaded member and flank angles of both sides of a thread ridge of one threaded member are smaller than a flank angle of a flank of a thread ridge of the other threaded member (basic ridge profile) (PTLS 5 and 6).
In both fastening members of (3) and (4), the thread ridge of one threaded member abuts the thread ridge of the other threaded member when fastening one threaded member and the other threaded member together, and a large frictional force is generated between one threaded member and the other threaded member by elastic deformation. Consequently, fastening by the threaded portion is prevented from being loosened.